My invention pertains to a pulse code system for transmitting data through the rails of a railroad track section. More particularly, the invention pertains to a unique pulse code system for transmitting, through the rails included in a railroad track circuit, data including both information and commands in addition to the functions of train detection and movement control.
Pulse codes, for example of an on/off direct current energy type with rates below 7 Hz, have long been used in track circuits in railroad signaling systems. These DC coded track circuits detect the presence or absence of trains within the circuit and transmit indications of advance traffic conditions which control the signals governing the train movements. The length of such track circuits may be as much as 15,000 feet which is a distinct advantage in high speed signaling systems. Such track circuits have been highly successful even though they transmit a limited amount or scope of information. One problem which has been solved over the years is that of the energy storage effect in the rails which is equivalent to a resistor-capacitor series network across the rails tending to prolong the on-time, that is, the energy on periods, of the code. Such track circuits are normally provided with a resistor shunt to quickly drain this charge from the rails during each energy off period. On occasion, a modulated alternating current may be used as the rail current, that is, the code pulses are of alternating current of a selected frequency. Such pulses may be used to control cab signals carried on the trains in addition to control of the wayside signals. Such alternating current coded track circuits are of shorter weight because of the high rail attenuation to the alternating current. It is desirable, of course, to replace the coding and decoding relays with solid state devices. However, direct substitution into the DC coded track circuit of such devices creates interfacing problems because of the track storage characteristic. Isolation between the rails and the solid state devices is also required to provide transient protection and noise reduction. Solutions to overcome the energy storage problem are possible but are complicated by the necessity for using an added means to shunt the rails during the off periods of the code pulses. The possible alternative is a bi-polar code similar to a DC pulse code but including a plurality of pulses in each code transmission. In other words, each code group includes a selected number of pulses so that the track energy storage effect is substantially eliminated within each code transmission. The result is a low frequency alternating current so that transformer coupling to the rails from the wayside apparatus is possible. This solves the interface and isolation requirements and makes it possible to transmit an increased amount of data through the rails of the track circuit.
Accordingly, an object of my invention is an improved pulse code system for transmitting data through the rails of a railroad track section.
Another object of the invention is pulse code apparatus for transmitting data through the rails of a railroad track using a code format which eliminates the track storage energy factor.
Also an object of my invention is a pulse code system which transmits data through the rails of a track circuit by a bi-polar code having a selected number of pulses with the pulse length designating the character of each pulse.
A further object of the invention is a pulse code system for transmitting information through the rails of a railroad track with a low frequency alternating current which is effectively a bi-polar direct current code with a predetermined number of pulses in each group with selected length characteristics to determine the data transmitted.
It is also an object of my invention to provide a code system for a railroad track section in which a bi-polar pulse code is used to transmit information through the rails with individual pulses having selected length characteristics to create a pattern which eliminates track energy storage distortion.
Yet another object of the invention is apparatus to transmit data in either direction through the rails of a railroad track section in which the operation of the power supply at each location to supply operating energy to the apparatus is dependent on the reception from the central data processor unit of a check signal indicating the correct operation of all elements of the system.
A still further object of my invention is a pulse code system for a railroad track section in which a low frequency alternating current in the form of bi-polar code pulses is alternately transmitted from each end, successive pulses in each code group being of opposite polarity and having selected lengths, long or short, to form a pattern which designates the data transmitted, a central processing unit at each location decoding the received pulses to register the data and checking the correct operation of each system element, this processing unit also providing a check signal, which maintains the apparatus power supply active to provide operating energy, only when correct operation of the total system is assured.
Other objects, features, and advantages of the invention will become apparent from the following specification and appended claims when taken in connection with the accompanying drawings.